1. Field of the Invention
This invention relates to improvements in matrix display devices of the high-density cellular type in which each element of a display is controlled by an individual cell enclosing a shutter electromagnetically movable between a position in which it opens and a position in which it closes an aperture through which, when open, light is visible to an observer. A device of this kind is described in U.S. Pat. No. 3,562,938.
2. Description of the Prior Art
Hitherto, cell matrices for display devices of the high-density cellular type have been constructed bonding together continuous plastics sheets, one of which is apertured to form the individual cells of the matrix, each of which cells may, for instance, contain a loose electro-magnetically movable shutter member. The matrix assembly has then been bonded to a sheet of glass to provide support and ensure flatness of the matrix. The glass sheet supporting the matrix has then been mounted in a cabinet frame which serves as a housing for the display. The floor of the cabinet frame includes a rail which guides a movable assembly of electromagnetic heads and determines its height relative to the cells of the display. It is necessary that each of the electro-magnetic heads in the assembly shall follow a path in good alignment with an individual horizontal row of the matrix cells, in order to ensure correct operation of the display, since movement of each shutter between its open and closed positions is effected by appropriate selective energisation of the electromagnet appropriate to the cell rank containing that shutter, as the head assembly traverses the matrix.
The construction described above has disadvantages which it is the object of the present invention to overcome. These disadvantages are as follows:
(1) the display assembly is heavy and fragile because it includes a glass sheet;
(2) inaccuracy of registration between the individual heads and the respective rows of cells in the matrix may arise as a result of:
(a) the assembly of plastics sheets forming the matrix being itself not straight;
(b) the presence of manufacturing tolerances in the operation of bonding the matrix assembly to the glass sheet;
(c) the extruded member forming the rail which supports the head assembly may itself not be straight, but subject to initial manufacturing tolerances, and curvature of the rail may be opposite to that of the plastics matrix assembly.